The present invention relates generally to harmonic regulation of a power conversion system and, more specifically, to a method and system of canceling and injecting harmonics into a power conversion signal.
Active filters employing active-feedback loops are increasingly being used to eliminate selected harmonic errors within a power signal of a power conversion or power line conditioner system. Utilizing a feedback loop and an inverter, such active filters are able to minimize the differences between an instantaneous signal and a desired signal. The differences between the instantaneous signal and the desired signal are indicative of the distortion found or created in the signal caused by various loads in the electrical network. Oftentimes, the loads are nonlinear in nature which further accentuates the distortion in the instantaneous signal.
Generally, nonlinear loads cause reflected harmonics to flow back into a power source resulting in typically unwanted harmonics in the electrical network. The active filter is used to reduce these unwanted harmonics using series and/or parallel power conversion stages. Known active filters reduce or cancel the harmonic effects in the power conversion signal by implementing a harmonic regulator that applies a Clarke-Park transformation techniques to convert desired feedback signals to a reference frame synchronous with the harmonic of interest. In these known active filters, the transformed feedback signal containing the unwanted harmonics may contain AC components of other harmonics (including the fundamental) thereby requiring a low pass filter to remove unwanted frequencies in the signal. Further, these known active filters do not permit the displaying of the 1 harmonic magnitudes determined by the Clarke-Park transformation without low pass filtering to eliminate AC components from the transformed signal. Additionally, known filtering systems do not allow for arbitrary references to control any desired harmonic to a zero or non-zero value thereby permitting the driving of the harmonics in the feedback signal to a non-zero value.
It would therefore be desirable to have a system and method capable of canceling and/or injecting harmonics into a power conversion signal. It would further be desirable to design a system and method capable of displaying the magnitudes of harmonic coefficients determined by a discrete Fourier transformation and to complete the discrete Fourier transformation using a resettable integrator over a single signal period without low pass filtering.
The present invention discloses a method and system of harmonic regulation that overcomes the aforementioned drawbacks. In one aspect of the present invention, a method of harmonic regulation for generating a multiphase electrical reference signal is disclosed. The method includes the step of determining at least one reference harmonic coefficient and identifying an energizing signal having a plurality of harmonics. The method further includes the step of selecting at least one harmonic of the energizing electrical signal and determining at least one harmonic coefficient of the at least one harmonic of the energizing electrical signal over one signal period. The method further includes the step of generating the multiphase electrical reference signal from the previously determined at least one harmonic coefficient.
In accordance with another aspect of the present invention, a method of harmonic regulation for a power conversion system is disclosed. The method includes the steps of determining at least one reference harmonic coefficient and receiving at least one reference input electrical signal and at least one feedback electrical signal. An electrical error signal is then determined from the at least one reference input electrical signal and the at least one feedback electrical signal. Next, the method selects at least one harmonic having at least one coefficient from the electrical error signal and determining an electrical angle, Be. The method then determines a sine signal and a cosine signal of the selected at least one harmonic at the known inverter electrical angle and integrates the sine signal and the cosine signal over one signal time period, T. The signal time period T is equivalent to the reciprocal of the inverter base frequency. The integrated sine signal and the integrated cosine signal are then compared to the at least one reference harmonic coefficient and at least one harmonic axis value is determined therefrom. The method further includes the step of injecting the at least one harmonic axis signal into a power conversion system.
In yet another aspect of the present invention, a harmonic regulator is disclosed. The harmonic regulator includes a feedback signal detector configured to determine a feedback error signal and further configured to determine an electrical angle corresponding to a selected harmonic and further configured to determine a feedback signal period. The harmonic regulator further includes a harmonic selector configured to select a feedback error signal harmonic. A resettable integrator configured to determine at least one harmonic coefficient of the at least one error signal harmonic is further provided wherein the at least one harmonic coefficient is determined over a single feedback signal period. The harmonic regulator further includes at least one adder configured to determine a difference of the at least one harmonic coefficient and the at least one reference harmonic coefficient. A regulator is provided and configured to amplify and integrate the difference and is further configured to determine at least one harmonic axis reference signal. An inverse rotator is provided to receive the at least one harmonic axis reference signal and to generate an inverse rotator output. The harmonic regulator further includes at least one summer configured to determine a final electrical reference signal from the inverse rotator output and an inverter current reference output.
In yet a further aspect of the present invention, a power conversion system is provided. The system includes a number of electromagnetic interference (EMI) filters, an AC/DC converter, a DC link filter, a DC/AC inverter, an AC filter, a plurality of feedback sensors including a plurality of voltage feedback sensors and 4 current feedback sensors, and a feedback loop that includes a number of voltage and current feedback sensor conditioners. The power conversion system further includes an inverter control having a harmonic regulator including a resettable integrator wherein the harmonic regulator is configured to determine at least one reference harmonic coefficient and identify a distortion signal having a plurality of harmonics. The harmonic regulator of the power conversion system is further configured to select at least one harmonic of the distortion signal and determine at least one harmonic coefficient therefrom over a single signal period. The harmonic regulator is further configured to generate a multiphase electrical reference signal for the power conversion system.
In an another aspect of the present invention, a computer program comprising a set of instructions to cause one or more computers to inject at least one harmonic axis signal into a power conversion system. The computer program further causes the one or more computers to determine at least one reference harmonic coefficient and further causes the one or more computers to receive at least one reference electrical signal and at least one instantaneous electrical signal. The set of instructions of the computer program further causes the one or more computers to determine an electrical error signal from the at least one reference electrical signal and the at least one instantaneous electrical signal. The computer program further cause the one or more computers to select at least one harmonic having at least one coefficient from the electrical error signal and to apply a discrete Fourier transformation to the at least one harmonic selected to determine a first integrated signal and a second integrated signal. The one or more computers are then caused to compare the first integrated signal and the second integrated signal to the at least one reference harmonic coefficient and to determine at least one harmonic axis signal therefrom. The computer program then causes the one or more computers to inject the at least one harmonic axis signal into the power conversion system.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.